tests: add httpcommon tests and add new file_handler methods

[ReenigneArcher]

Description

Add tests from #2613

Todo:

• Update download file function, automatically create the directory if it doesn't exist.

Screenshot

Issues Fixed or Closed

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

Branch Updates

LizardByte requires that branches be up-to-date before merging. This means that after any PR is merged, this branch
must be updated before it can be merged. You must also
Allow edits from maintainers.

• I want maintainers to keep my branch updated

[codecov]

Codecov Report

Attention: Patch coverage is 61.11111% with 7 lines in your changes missing coverage. Please review.

Project coverage is 8.97%. Comparing base (0c0b4c4) to head (5491e73).
Report is 148 commits behind head on master.

Files with missing lines	Patch %	Lines
src/httpcommon.cpp	20.00%	1 Missing and 3 partials ⚠️
src/config.cpp	0.00%	0 Missing and 1 partial ⚠️
src/confighttp.cpp	0.00%	0 Missing and 1 partial ⚠️
src/file_handler.cpp	90.90%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #2712      +/-   ##
=========================================
+ Coverage    8.73%   8.97%   +0.23%     
=========================================
  Files          94      94              
  Lines       17373   17389      +16     
  Branches     8251    8267      +16     
=========================================
+ Hits         1518    1560      +42     
+ Misses      12995   12967      -28     
- Partials     2860    2862       +2     

Flag	Coverage Δ
Linux	6.79% <46.66%> (+0.29%)	⬆️
Windows	4.16% <62.50%> (+0.33%)	⬆️
macOS-12	10.04% <29.41%> (+0.23%)	⬆️
macOS-13	9.95% <29.41%> (+0.22%)	⬆️
macOS-14	10.25% <29.41%> (+0.23%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/config.cpp	4.78% <0.00%> (+<0.01%)	⬆️
src/confighttp.cpp	0.77% <0.00%> (+<0.01%)	⬆️
src/file_handler.cpp	84.00% <90.90%> (+5.42%)	⬆️
src/httpcommon.cpp	26.08% <20.00%> (+23.03%)	⬆️

[ReenigneArcher]

@mariotaku FYI